A metallic oxide such as an indium tin oxide (ITO) has been used in a transparent conductive film in which light transmittance is required. Examples of such a transparent conductive film include a transparent conductive film provided on a display surface side of a display panel, and furthermore a transparent conductive film of an information input device arranged on the display surface side of the display panel. However, the transparent conductive film using a metal oxide is formed by sputtering in a vacuum environment, thereby increasing manufacturing cost. In addition, in the transparent conductive film, crack and delamination have been likely to occur due to deformation such as bending and distortion.
Therefore, in place of the transparent conductive film using a metal oxide, a transparent conductive film using a metal nanowire, which can be formed by coating or printing and also has a high resistance to bending and distortion, is considered. The transparent conductive film using a metal nanowire has also attracted attention as a next-generation transparent conductive film without using indium being a rare metal (for example, see Patent Literatures 1 and 2 and Non-Patent Literature 1 below).
However, when the transparent conductive film using a metal nanowire is provided on the display surface side of the display panel, outside light reflects diffusely on the surface of the metal nanowire, so that a so-called black floating phenomenon in which a black display of the display panel is displayed slightly bright occurs. The black floating phenomenon causes deterioration of display properties due to reduced contrast.
For the purpose of preventing occurrence of such black floating, a gold nanotube using gold (Au) on which diffused reflection is unlikely to occur has been proposed. The gold nanotube is formed by first using as a template a silver nanowire which is likely to reflect light diffusely, and then performing gold plating on the silver nanowire. Thereafter, a silver nanowire portion used as a template is subjected to etching or oxidation, thereby allowing it to be converted into a gold nanotube (see, for example, Patent Literature 3 described below).
Furthermore, a method of preventing light scattering by using a metal nanowire and a secondary conductive medium (such as a CNT (carbon nanotube), a conductive polymer, and an ITO) in combination has been proposed (see, for example, Patent Literature 2 described below).